docs: improve benchmark links and memory units

[zhangzhenghao]

Summary

• link the README benchmark image to the benchmark site
• open generated SVGs in a new tab instead of downloading them
• chart peak resident memory in bytes while formatting hover values as readable MB/GB units

Verification

• pnpm test
• pnpm check
• pnpm build
• inspected generated export link attributes and SVG memory labels

[cloudflare-workers-and-pages]

Deploying xvec with    Cloudflare Pages

Latest commit:	8fe9175
Status:	✅  Deploy successful!
Preview URL:	https://fe85c1f5.xvec.pages.dev
Branch Preview URL:	https://docs-benchmark-links.xvec.pages.dev

View logs

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.38%. Comparing base (b3a9ff8) to head (8fe9175).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #89      +/-   ##
==========================================
- Coverage   81.66%   81.38%   -0.29%     
==========================================
  Files         148      148              
  Lines       30253    30253              
==========================================
- Hits        24706    24621      -85     
- Misses       5545     5630      +85     
  Partials        2        2              

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